A plurality of unspecified cavities such as a corrosion cavity of a limestone zone, an artificial cavity of an abandoned mine, etc. has increasingly caused damage to human life and social overhead capital including an above ground structure such as a road, a railroad and a bridge. Particularly, a construction site is in many difficulties such as a great expense for changing the existing design and preparing new countermeasures to avoid an underground cavity, and so on. Thus, a ground reinforcement to a ground subsidence zone has emerged as an important issue.
The ground reinforcement to the limestone zone has been designed and constructed within a range of economically securing the stability of the existing facilities or a structure to be newly build rather than reinforcing the ground with regard to the whole cavity. To prevent the ground subsidence of the dangerous zone and secure the stability of the structure, an underground-cavity filling method based on cement mortar grouting has been mostly used in Korea.